Cuesta College, San Luis Obispo, CA
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LeviNeuzerling
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(A) w.
(B) Fdrag.
(C) (Both of the above choices.)
(D) (Neither of the above choices.)
Correct answer (highlight to unhide): (B)
There are two forces acting on the coffee filter stack just after it is released:
weight force w of Earth on stack (downwards),and as the coffee filter stack falls, its displacement (and direction of travel) points downwards.
drag force Fdrag of air on stack (upwards);
The work done by the weight force is given by:
Wweight = (w·cos(0°))·s,
where the tail-to-tail angle between the direction of the weight force (downwards) and the displacement (downwards) is 0°. Since cos(0°) = +1, the weight force does positive work on the coffee filter.
The work done by the drag force is given by:
Wdrag = (Fdrag·cos(180°))·s,
where the tail-to-tail angle between the direction of the drag force (upwards) and the displacement (downwards) is 180°. Since cos(180°) = –1, the drag force does negative work on the coffee filter.
Sections 70854, 70855
Exam code: quiz04w33N
(A) : 22 students
(B) : 24 students
(C) : 1 student
(D) : 1 student
Success level: 50%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.89
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